1. Field of the Invention
The present invention relates to a color sensor that detects color components.
This application claims priority to and the benefits of Japanese Patent Application No. 2009-267707 filed on Nov. 25, 2009, the disclosure of which is incorporated herein by reference.
2. Background Art
When various scenes are photographed by a photographing device such as a digital camera or a digital video camera in which a solid-state imaging element is mounted, photographing is performed under various illuminating light sources. A technique is known in which a color sensor is mounted along with an imaging element, a type of photographing light source is accurately identified, and good white balance is implemented regardless of the light source under which photographing is performed.
FIG. 13 is a cross-sectional view of a color sensor of the related art. In an example shown, the color sensor includes a first color filter 81, a second color filter 82, a third color filter 83, a silicon substrate 84, a first photodiode 85, a first separation layer 86, a second photodiode 87, a second separation layer 88, and a third photodiode 89. A portion covered by the first color filter 81 becomes a first pixel, a portion covered by the second color filter 82 becomes a second pixel, and a portion covered by the third color filter 83 becomes a third pixel.
For example, the first color filter 81 is a color filter that transmits red light and is arranged to cover the first pixel. For example, the second color filter 82 is a color filter that transmits blue light and is arranged to cover the second pixel. For example, the third color filter is a color filter that transmits light having a green light and is arranged to cover the third pixel.
The first photodiode 85 is a photoelectric conversion element that photoelectrically converts light incident through the first color filter 81, and is arranged on the silicon substrate 84. The second photodiode 87 is a photoelectric conversion element that photoelectrically converts light incident through the second color filter 82, and is arranged on the silicon substrate 84. The third photodiode 89 is a photoelectric conversion element that photoelectrically converts light incident through the third color filter 83, and is arranged on the silicon substrate 84.
The first separation layer 86 separates the first pixel and the second pixel. The second separation layer 88 separates the second pixel and the third pixel. By this configuration, the first, second, and third pixels can respectively detect different color lights. Thereby, the color sensor can detect incident light components. For example, if the color sensor of this configuration is used in a digital camera or the like, the digital camera can identify a type of light source on the basis of the light components detected by the color sensor.
A color sensor is known which has a pixel having sensitivity to light of a wavelength of 500 to 530 nm as a fourth pixel as well as the pixels having sensitivities to wavelength bands of color lights of red (R), green (G), and blue (B) (for example, see Japanese Unexamined Patent Application Publication No. 2004-64413).
FIG. 14 is a graph showing relative the sensitivity of light detected by a pixel having sensitivity to a wavelength band of red light, the relative sensitivity of light detected by a pixel having sensitivity to a wavelength band of green light, the relative sensitivity of light detected by a pixel having sensitivity to a wavelength band of blue light, and the relative sensitivity of light detected by a fourth pixel.
As shown, the pixel having the sensitivity to the wavelength band of the blue light detects most light whose wavelength is about 455 nm. The pixel having the sensitivity to the wavelength band of the green light detects most light whose wavelength is about 540 nm. The pixel having the sensitivity to the wavelength band of the red light detects most light whose wavelength is about 620 nm. The fourth pixel detects light whose wavelength is 500 to 530 nm. Thus, the color sensor has the fourth pixel that detects light of a wavelength other than wavelengths of most lights to be detected by the pixels having sensitivities to wavelength bands of color lights of R, G, and B, thereby detecting light components with higher accuracy.
In the color sensor of the related art, crosstalk (wraparound of a charge) occurs in the photoelectric conversion element (a photodiode). Thereby, there is a problem in that the accuracy of light component detection by the color sensor is degraded.
Hereinafter, the crosstalk occurring in the photoelectric conversion element of the color sensor will be described. FIG. 15 is a schematic diagram illustrating the crosstalk occurring in the photoelectric conversion element of the color sensor. In an example shown, the color sensor includes a first color filter 91, a second color filter 92, a silicon substrate 93, a first photodiode 94, a second photodiode 95, and a separation layer 96. A portion covered by the first color filter 91 becomes a first pixel, and a portion covered by the second color filter 92 becomes a second pixel.
For example, the first color filter 91 is a color filter that transmits long-wavelength light, and is arranged to cover the first pixel. For example, the second color filter 92 is a color filter that transmits short-wavelength light, and is arranged to cover the second pixel. The photodiode 94 of the first pixel is a photoelectric conversion element that photoelectrically converts light incident through the first color filter 91, and is arranged on the silicon substrate 93. The photodiode 95 of the second pixel is a photoelectric conversion element that photoelectrically converts light incident through the second color filter 92, and is arranged on the silicon substrate 93. The separation layer 96 separates the first pixel and the second pixel.
In the photoelectric conversion element configured as described above, for example, the first photodiode 94 generates a photo charge 97 in a deep position of the silicon substrate 93 if the first color filter 91 transmits the long-wavelength light. The photo charge 97 generated in the deep position of the silicon substrate 93 is diffused like photo charges 97-1 to 97-3, and wraps around into the second photodiode 95. Thus, the second photodiode 95 detects the photo charge 97 generated by the first photodiode 94. There is a problem in that the accuracy of light component detection of the color sensor is degraded by the above-described crosstalk.
An object of the present invention is to provide a color sensor capable of suppressing the degradation of detection accuracy of light components due to the effect of crosstalk and detecting the light components with higher accuracy.